Recent Results from the COBE Differential Microwave Radiometer

Abstract

The scientific objective of the COBE Differential Microwave Radiometer (DMR) investigation is to use the cosmic microwave background (CMB) radiation as a probe of cosmology. Stringent limits can be set on the amplitude of fluctuations of the potential energy at the surface of last scattering of the CMB photons. Large angular scale (>1 .) fluctuations in the gravitational potential energy are directly related to temperature anisotropies in the CMB by the Sachs-Wolfe Effect (Sachs & Wolfe 1967), which describes the gravitational redshift of photons as they are last scattered at a gravitational potential energy per unit mass, ϕ, giving δϕ/c2 = 3δT/T. The DMR instrument was described by Smoot et al. (1990), recent scientific results by Smoot et al. (1991a,b), and calibration by Bennett et al. (1991). The DMR consists of two independent radiometers at each of three frequencies: 31.5, 53, and 90 GHz. Each radiometer measures the difference in temperature between two 7. FWHM beams separated by 60.. The scanning pattern of the instrument causes all 60. separation pixel-pairs to be observed thousands of times.